As is known in the art, many electrical systems include a power supply system and more particularly to power supply systems having a plurality of power supply units, one of such units being provided for redundancy in the event of a power supply unit failure. Such power supply systems are sometimes referred to as N+1 power supply systems where N is the number of units used in normal operation and the “1” refers to the redundant power supply unit. Thus, N may be one or more than one.
As is also known in the art, with an N+1 power supply systems it is difficult to detect a latent fault with either one of the power supply units or the cabling which connects a unit to a common power bus. More particularly, N+1 power supply systems typically have internal logic OR-ing diodes to interconnect the individual power supply units to the common power bus. If one of the N+1 power supply units fails it would be desirable to isolate the particular one of the N+1 power supply units that has failed. This is of particular use for standby voltage rails, which do not have any additional means of detecting or isolating failure.